The present invention relates generally to a system for coating discontinuous fibers with a liquid coating material, and more particularly to an improved apparatus and method of applying a liquid coating material to discontinuous fibers to provide coated fibers.
A number of techniques for applying binders to webs of fibers are known, and are disclosed in U.S. patent application Ser. Nos. 07/673,685 now abandoned, and 07/673,899 now U.S. Pat. No. 5,432,000, each of which are entitled "Binder Coated Discontinuous Fibers with Adhered Particulate Materials," each of which are continuation-in-part applications of U.S. patent application Ser. Nos. 07/326,188 now U.S. Pat. No. 5,230,959, entitled "A Coated Fiber Product With Super Absorbent Particles;" 07/326,181 now abandoned, entitled "A Natural Fiber Product Coated With A Thermoset Binder Material;" and 07/326,196 now abandoned, entitled "A Natural Fiber Product With A Thermoplastic Binder Material," and each of these five patent applications are commonly owned by the assignee of the present invention and are hereby incorporated by reference herein.
Other blending/mixing operations have been used in other applications. One such blending operation is known as blow line blending. During blow line blending, binder mixing and some deagglomeration of fibers may occur during "the blow" cycle. However, the blow cycle offers only one opportunity for such mixing and deagglomeration to occur. Furthermore, control of the coating and the production of bulk fibers which are substantially continuously coated is not available in blow line blending. Thus, blow line blending has many disadvantages rendering it undesirable for the coating of fibers.
Another known blending/mixing operation is performed during the manufacture of particle board and flake board. However, the low speed mixing used during the particle board/flake board manufacture has little or no deagglomeration characteristic. In most composite particle or flake boards which are pressed together after mixing, deagglomeration simply is not a concern. There are some high speed mixers used in the particle board/flake board industry, but these mixers have inadequate mixing rates and inadequate deagglomeration capabilities to suitably continuously coat fibers. Furthermore, these systems tend to produce agglomerated fibers and not individual fibers.
Another blending/mixing operation is known as slurry or liquid state mixing. In liquid state mixing, however, fiber agglomeration takes place. Furthermore, the majority of commercial available mixers are designed for liquid state mixing, and thus, the problem of deagglomeration is simply not addressed by mixer vendors.
In the past, fluidized beds have been used for coating various types of particles, such as pills and granules. However, such coating methods are not understood to have been considered for coating discontinuous fibers, perhaps because it would be anticipated that such fibers do not readily fluidize, would flocculate and would agglomerate during the coating process.
Other coated fiber production methods employ variations on traditional batch methods. For example, current in-line processes are duct work oriented, and disadvantageously require space consuming relatively long ducts or recirculating duct work systems. These in-line methods also require implementation of in-line break-up methods to correctly form acceptable coated fibers.
Thus, a need exists for an improved fiber hopper/blender system and method for applying a liquid coating material to discontinuous fibers, which is directed toward overcoming the above limitations and disadvantages of the prior art.